Beverage containers such as soda or beer cans are currently marketed with self contained openers in the form of lift tabs. In all of the present embodiments, the lift tab is comprised of a ring portion for control by an inserted finger. In one form of lift tab, the ring is attached to a pear shaped prescored section of the container top, with continued lifting of the ring causing the pear shaped section to become completely detached from the container top. This type of lift tab has however met with an environmental outcry since it has resulted in a new type of litter. Accordingly, a more acceptable non-detachable lift tab is presently being utilized on nearly all of the soda and beer cans currently sold in the United States, with the soda and beer cans being themselves recycled to reduce litter.
The non-detachable lift tab, with some design variations, is basically comprised of a short, somewhat rectangular, elongated aluminum strip (about 1.times.9/16 inch--25.times.16 mm) with rolled over edges for structural strength and for prevention of exposed sharp edges. There has been a tendency to reduce the dimensions of the tab to save on material costs.
At a first end, the tab is formed into a ring-like member (also with rolled over inner edges) for finger insertion and lifting. The second end, with strengthened rolled over edge, is rounded or tapered (with some tabs the pushing end is a straight edge) and crimped for force-concentrated pushing engagement with a cantilevered weakened section of the container top, which will open upon continued application of pressure. To facilitate manufacture and container storage nesting, the usually circular container top is shallowly dished along a major portion of a diameter thereof. About half of the length of the dished area is formed for seated mating with the lift tab, i.e slightly larger but conformed to the peripheral shape of the lifting end and adjacent sides of the lifting tab. The center of the container top, situated within the dished area, is formed with an outwardly extending hollow rivet-like section which fits into a corresponding aperture located on the longitudinal axis of the tab. The aperture is positioned on the tab such that the engagement between tab and container top results in about three quarters of the length of the tab (the lifting end) being situated on one side of the engagement site and about one quarter of the tab (the pushing end) being situated on the other side. The rivet-like section is then peened over, during assembly, to fixedly attach the lift tab to the container top.
The remaining dished area in the container top contains a weakening score line in the shape of a thumb nail (other design related shapes include truncated ovals or circles) having its tapered (or arced) end extending in a direction opposite that of the tab. A small portion of the "thumb nail", peripherally adjacent to the engagement site, however remains unscored. The pushing end of the tab extends over the non-scored portion and over the adjacent area enclosed by the thumb nail score line. During the opening operation, the lifting end of the tab is elevated. The tab pivots through the rivet engagement area and the pushing end of the tab swivels down thereby tearing and pushing the weakened area of the container top into the container. Because of its proximity to the pushing end of the tab, the scored area, adjacent the rivet-like section, tears open first, with initial internal gas pressure relief (the contained beverages are usually carbonated or are susceptible to internal gas evolution). Upon continued pushing pressure, the tear propagates around the score line away from the pushing end of the tab. The section of the container top, enclosed by the score line, then pivots down into the container in a cantilevered movement, and is held from falling into the container by the small unscored section of the "thumb nail". The area surrounding the contact point between the tab end and the container top is strengthened by a raised rib integrally formed within the "thumb nail" area to prevent gouging of the container top by the tab end.
In order to prevent detachment or breakage of the tab, at the peened over portion, the tab itself is partially circumferentially lanced or slotted around the engagement site. The lance line or slot extends from the lifting end of the tab to equidistant points just beyond the peened over engagement site and on both sides thereof. The partial circumferential lance line or slot also slightly overlaps the thumb nail score of the container top. The connecting line between the ends of this lance line or slot defines the pivoting or fulcrum line (slightly removed from the peened over rivet section) for the pushing end of the tab and all the pivoting or fulcrum pressure is concentrated on this pivoting line. Initial lifting of the tab through the pivoting line is relatively strongly resisted by engagement of the pushing end of the tab with the container top and the pressure required to open the score line in the container top. Such resistance is even greater if the contents of the container are also pressurized. In addition, the increased tendency toward shorter tabs has reduced the leverage of the tab with concomitant increase in resistance to lifting.
This relatively high resistance results in significant consumer inconvenience particularly since the lifting end of the tab is near the obstructing raised edge of the seal between the container top and the container. In addition, access to the tab is further obstructed by the tab being slightly lowered into the dished area of the container top. Insertion of a finger for lifting the tab is impeded and the small purchase area initially available is resisted by the relatively high resistance with the very real likelihood of fingernail breakage. Such resistance is, of course, negligible if the full finger can be utilized for lifting. In order to obviate this problem some lift tabs are provided with an elevated ring tab. However, the degree of elevation is limited by increased difficulty in manufacturability and the fact that the container tops are designed to be stacked for storage and production line feeding. Thus, an overly elevated tab will either be bent or will impede proper stacking and such elevation cannot be more than about 1/8 of an inch (3 mm) whereas about 1/4 inch (6 mm) is required for effective finger purchase on the lifting end of the tab. Other means for providing the initial lift for full finger purchase include the use of coins, keys and special tools which are small enough to be inserted under the tab and then used as small levers.
It is noted that the previously used detachable (but environmentally objectionable) tab offered little or no resistance pressure to moving the tab into a perpendicular position, for full finger grasp, prior to the lifting off opening.